The present invention relates to an exhaust flap for an exhaust system of an internal combustion engine. Exhaust flaps of this type serve for closing the exhaust duct of an exhaust system. It may be desirable, in this context, to close the entire cross section of the exhaust duct by means of the exhaust flap. It is just as possible, however, to close only a partial region of the cross section of the exhaust duct by means of the exhaust flap. It is also possible, furthermore, to subdivide the exhaust duct into a plurality of partial ducts and also connect these partial ducts in parallel. The exhaust flap according to the invention is then also suitable for closing such a partial duct completely or partially, while the parallel partial duct can operate without an exhaust flap. The exhaust flaps are conventionally designed in such a way that they can be tilted either in various steps or continuously, in such a way that the initially closed cross section of the exhaust duct can be opened. In particular, it is possible for the exhaust flap to be tilted back and forth between a closing position, wherein the exhaust duct is completely closed, and an opening position, wherein the exhaust duct is completely open.
The exhaust flaps according to the invention can be used both in the hot and in the cold region of the exhaust system. A typical field of use is the function as a valve, for example for controlling a bypass in order to bypass a heat exchanger or catalyst. Another typical field of use is the closing of an end pipe. Finally, it is also customary, in the area of sound damping, to open and close various flow paths within the silencer with the aid of exhaust flaps.
In this context, German patent DE 199 35 711 C discloses a silencer with an exhaust flap, wherein an actuating element is acted upon directly by the exhaust-gas stream in order to actuate a closing element forming the actual exhaust flap. One disadvantage of that configuration is the need to have to provide both an actuating element and a closing element. To be precise, these parts are very costly, because, on account of the leak tightness and corrosion and heat resistance required here, the mounting of parts moveable in this way is highly complicated and therefore very costly. The above-mentioned publication also mentions directly controlling flap systems, wherein the exhaust-gas stream acts directly upon the exhaust flap. However, it is disadvantageous with the configurations mentioned there that they do not allow a stable operating behavior or increase the exhaust-gas backpressure too sharply when there is a high gas throughput.
It is accordingly an object of the invention to provide an exhaust flap for closing an exhaust duct, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which has a further simplified configuration, and at the same time ensures stable operating behavior.
With the foregoing and other objects in view there is provided, in accordance with the invention, an exhaust flap for closing an exhaust duct conducting an exhaust-gas stream, the exhaust flap comprising:
a closure plate directly impinged by the exhaust-gas stream and disposed to at least partially close a cross section of the exhaust duct; and
a flow body disposed adjacent the closure plate and to be impinged by the exhaust-gas stream, the flow body forming an actuator for the exhaust flap.
The basic idea of the invention is to provide on the exhaust flap a closure plate performing the closing function and also to arrange a flow body additionally next to the closure plate. The closure plate and the flow body are consequently connected to one another and also pivot synchronously with one another as parts of the exhaust flap. In this case, as regards a rectangular closure plate, the flow body may be arranged next to each of the four sides of this rectangle. The closure plate may in this case be configured in such a way that, in the closing position, it closes the exhaust duct completely. It is just as possible by means of the invention to close only a part region of the cross section of the exhaust duct. Since the closure plate is arranged directly in the exhaust duct, the exhaust-gas stream also impinges directly onto the closure plate inner face confronting it. The exhaust-gas stream consequently exerts a dynamic pressure on the inner face of the closure plate. This dynamic pressure is utilized as the opening force for the closure plate and consequently for the exhaust flap. As a result of the dynamic pressure exerted on the closure plate, the exhaust flap can open up to a particular opening angle. Practical tests have yielded the result that, for example on acoustically active exhaust flaps, an opening angle of about 30xc2x0 can be achieved with the aid of the dynamic pressure. The dynamic pressure exerted on the inside of the closure plate is not sufficient, however, for opening the exhaust flap completely, particularly because the opening movement of the exhaust flap is additionally impeded by the force of a return element usually designed as a return spring.
As soon as the exhaust flap opens and the flow body is no longer concealed, the exhaust-gas stream begins to flow onto the flow body arranged next to the closure plate. As a result of this flow onto the flow body, the exhaust flap is opened further, so that the flow body takes effect as an actuator for the exhaust flap. Stable operating behavior of the exhaust flap is ensured in this way. Another advantage of the invention is that no further moveable parts which have to be mounted in a complicated way are present in addition to the exhaust flap. Instead, the exhaust flap is designed as an integral structural part which fulfils at the same time both the actuating function and the closing function of an exhaust flap.
In accordance with an added feature of the invention, the exhaust flap is arranged at an end of a duct portion of the exhaust duct and pivotally mounted counter to a biasing force which may be provided by a return element, such as a return spring disposed to force the exhaust flap to close off the exhaust duct. The fact that the exhaust flap is arranged in the exhaust duct at the end of a duct portion renders it possible, for example, to connect a plurality of parallel exhaust duct portions in series in the manner of a register. The arrangement in the region of the end of a duct portion has the advantage that the mounting for the exhaust flap can be arranged outside the exhaust duct and therefore outside the exhaust-gas stream. The flow of the exhaust-gas stream in the exhaust duct is thereby not impeded by the mounting. It is also thus possible to adapt the size of the exhaust duct to the exhaust-gas stream and so optimize the flow behavior in the exhaust duct. Finally, it is advantageous to provide the exhaust flap with a return spring, in order to prevent an undesirable generation of noise, for example rattling during the closing of the flap or when the dynamic pressure exerted on the exhaust flap is relatively slight.
In accordance with an additional feature of the invention, the exhaust flap has a U-shaped cross section with U-legs each forming a flap side wall and the closure plate forming a U-crosspiece connecting the U-legs. This exhaust flap construction has a simple design and at the same time is highly effective. By virtue of its U-shaped cross section, the exhaust flap closes the exhaust duct highly effectively. This construction is further developed where the flap side walls extend in a fork-like manner for additionally holding the flow body therebetween. The walls thus form a fork-like receptacle of the flow body between the flap side walls. The inner faces of the flap side walls and the inner face of the closure plate act in the same way as a guide blade of a turbine in this design and thus assist the subsequent flow onto the flow body in a particularly advantageous way.
In accordance with another feature of the invention, the flow body is a planar plate enclosing an obtuse angle with a plane defined by the closure plate. Alternatively, the flow body is a curved plate disposed to form an angle of incidence with a plane of the closure plate. In a specifically preferred embodiment of the invention, the flow body is configured as an airfoil.
In other words, it is possible for the flow body to be designed likewise as a plane plate in a similar way to the closure plate. This is very simple in design terms. Alternatively to this, in order to improve the flow behavior, a curved shape of the flow body may also be considered. The airfoil embodiment is considered particularly expedient. In this case, in a similar way to the wing of an aircraft, there is first a flow onto the end face of the wing and the exhaust-gas stream is as it were divided into two. Since the exhaust-gas stream builds up a higher velocity on the topside of the wing than on the underside of the wing, the static pressure above the wing is lower than on the underside of the wing, thus having the effect of an additional lift of the wing and therefore of the exhaust flap, with the result that the exhaust flap is opened further. A complete opening of the exhaust flap can be achieved, in particular, in combination with the design of the flap side walls and of the closure plate in the manner of a turbine guide blade.
In accordance with a further feature of the invention, it is also possible to arrange a plurality of flow bodies next to one another. In this case, for reasons of space, it may be expedient to arrange the flow bodies in such a way that they operate simultaneously, that is to say are connected in parallel. It is just as possible, however, for the flow bodies to be arranged so as to be coordinated with one another in such a way that they take effect only in succession in the manner of a register connection. Finally, it is also possible to connect a plurality of flow bodies in series.
In accordance with a concomitant feature of the invention, the closure plate has a fixed end articulated to the exhaust duct and a free end opposite the fixed end, and the flow body or flow bodies is/are arranged at the free end, and a hinge joint and a return spring are arranged at the fixed end.
In other words, it is expedient to provide the pivot bearing for the exhaust flap at one end, the fixed end, and to arrange the flow body at the other end of the exhaust flap, to be precise at the free end facing away from the fixed end. In this way, the pivot bearing and the flow body are arranged far away from one another, so that the effective lever arm and therefore the torque acting on the exhaust flap during a flow onto the flow body are very high, thus ensuring a rapid and reliable opening of the exhaust flap.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in Exhaust Flap, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.